Xiphophorus fishes have been used as an experimental model for fundamental biomedical research for over 75 years. Eventually "mechanistic" hypothesis must be confirmed using intact animal model systems. Well-characterized diverse experimental animal models are best suited to provide this function. In our future scientific environment, diverse animal models that allow us to better understand complex heritable (multigenic) traits will be of considerable importance as we attempt to unravel the genetics underlying complex traits such as behavior and the components leading to alternative in life histories. This R24 proposal is designed to maintain and enhance the Xiphophorus Genetic Stock Center (XGSC). The XGSC has operated within the United States since the 1930's. The traditional strength of the Xiphophorus model involves the non-biased assessment of genetic inheritance patterns associated with complex (multi-genetic) phenotypes within intact animals. The extreme genetic variability among Xiphophorus species (26 known taxa) and capability of producing fertile interspecies hybrids allows chromosomal/marker inheritance to be followed in individual backcross hybrid progeny. Statistical analyses involving hundreds of animals in a cohort can be used to identify markers linked to any trait of interest, so long as the phenotype (as a singular trait or QTL) can be discerned between two parental lines/species and in hybrid progeny. This experimental system is increasingly useful to test hypotheses generated from analyses of whole animal genomes (see 39+ letters of support for the XGSC, appended). With these expectations in mind, it is reasonable to continue to provide pedigreed Xiphophorus fish and associated materials to research laboratories, to continue our progress in development of cryopreservation procedures to ensure long term availability of stocks, and to further develop contemporary genomic tools for research scientists using and/or anticipating use of this valuable vertebrate experimental model. Accordingly our specific aims are: (1) To preserve and enhance the Xiphophorus Genetic Stock Center and provide the research community with animals and materials from genetically managed lines according to the specifications of each investigator. (2) To develop an extensive database of expressed sequence tag (EST) markers. EST marker annotation and the databases will be made available to the community. (3) We will collate the Xiphophorus recombination gene map developed in the previous project period with the BAC minimal tiling path (BAC-MTP) physical map currently being constructed. (4) To continue development of technology allowing cryopreservation of Xiphophorus sperm samples and to provide a preservation program where the XGSC fish lines are maintained as cryopreserved specimens to protect their genetic heritage.